Reference is made to U.S. Pat. No. 3,868,184 and to my copending U.S. patent application Ser. No. 777,043, filed Mar. 14, 1977, which are incorporated herein by reference.
In the above mentioned patent there is shown an optical smoke detector with an owner-operated bell crank carrying a thin wire. In testing the smoke detector the wire is swung through the smoke detection zone where the light path from the exciting source and the view of the photocell coincide. Light is then scattered directly from the test wire to the photocell. Such a test wire can simulate a predetermined density of smoke satisfactorily but has the disadvantage of being very fine and flexible making it difficult to see and handle during manufacture. A larger wire would be less critical as to its location with respect to the light beam and photocell and the reflectance of its surface, but would also scatter far more light than smoke particles.
Accordingly it is the object of the present invention to provide a smoke detector with testing means which need not include a fine, fragile wire and which scatters light in a manner more representative of smoke.